An amount of heat energy is required when scrap as an iron and steel source is preliminarily preheated or conducted to any preliminary heating process. For the reason mentioned above, even if the scrap is conducted to any process of heating, the running cost for heating does not enjoy any merit, and it also requires an expensive investment to construct the heating apparatus.
Recently, the position of scrap as an iron and steel source has become more important from the viewpoint of recycling of resources. Therefore, research and development into the preheating and melting process of the scrap, which is advantageous for reducing the total heat energy required in the melting and refining thereof, is required so that the recycling of the scrap is efficiently conducted so as to effectively utilize it as an iron and steel source, and furthermore the reduction of heat energy is advantageously attained.
As a prior art in the technical field in scrap melting, "Electric Furnace", (published by Japan Iron and Steel Institute, No. 27, 28 Shiraishi Memorial Lecture "Strategy of Electric Furnace in Common Steel", November, 1994) discloses that the scrap melting increases the running cost of steel making due to high consumption of electric power, and this is attributed to reduction of heat efficiency after the flat bath stage (melt down stage). Furthermore, as a scrap melting process of a converter type, "Iron and Steel" (vol. 78 (1992), p520, published by Japan Iron and Steel Institute) discloses that the construction cost of the apparatus to treat an amount of an exhaust gas increases, and a converter is required after the melting process because the resultant hot metal is molten iron. U.S. Pat. No. 4,852,858 discloses a method for preheating of scrap with an exhaust gas of a refining furnace in which a shaft vessel for holding a raw material is disposed at the upper portion thereof. However, the technology is difficult to control so that the range of the refining condition becomes large. As a result, stabilization of product quality cannot sufficiently be obtained. As another shaft-type preheating furnace, Japanese Examined Patent Publication No. 6-46145 discloses that, although a high heat efficiency can be attained, the scrap fuses due to exposure to high temperature gas at the furnace bottom, with the result that the fused scrap requires oxygen cutting. The prior art furthermore discloses that the charging ratio and the heat efficiency decreases to ensure a space for a fire grate. As a rotary kiln for scrap preheating, Japanese Unexamined Patent Publication No. 6-228662 discloses that heat efficiency decreases due to a low charging ratio of the scrap although the scrap is difficult to fuse due to the usual rotation and transferring thereof. On the other hand, scrap containing no organic substance is ordinarily heated, with the result that the cost increases due to a requirement on scrap selection.
Hereafter, the important problem is to treat a gas containing dioxin generated at the time of preheating scrap containing organic substances such as vinyl chloride. It becomes very advantageous in the utilization of the scrap to solve the problem mentioned above. Therefore, research and development of an apparatus and method for processing a exhaust gas while preheating the scrap is required.